This invention relates to air sampling devices, and more particularly to sealable cartridges for time averaged sampling of ambient gases.
Concomitant with increasing public and industrial awareness of the deleterious effects of many gases heretofore thought relatively harmless, substantial efforts are being allocated to detection and elimination of the harmful gases. In accordance with the Occupational Safety and Health Act of 1970, Public Law 91-596, Dec. 29, 1970, 84 Statutes 1590, specific exposure limits are set forth for protection of workers. These standards are based on total exposure over an entire working shift, i.e., based on time weighted averages. In accordance with the legislation, compliance is monitored by drawing a known quantity (e.g., one liter) of ambient gas per hour for eight hours through a tube packed with charcoal. The contaminant gases are absorbed by the charcoal which later is eluted, in one of a variety of ways (e.g., with carbon disulfide solvent), and analyzed such as by a gas chromatograph, mass spectrograph, or analogous analytic methods.
Consequently, employers and the like who are required to meet these requirements (and to pass periodic testing by labor department officials) have need to monitor their working conditions on an ongoing basis, in an effective a manner as possible.
It is accordingly a general object of the present invention to provide apparatus useful for monitoring time weighted average exposure (commonly referred to as "TWA") in accordance with legislated standards.
The most common method presently utilized to obtain time weighted average exposure is to draw the gases through a glass tube packed with charcoal. Typically, the tubes are filled with alternate segments of activated charcoal and glass wool or the like, are often provided with a precision locking spring and porous polyurethane plugs to hold the material in place, and are drawn and sealed at either end. For use, the drawn tips are broken off, after which flexible plastic sealing caps are mounted over the drawn portion.
The glass tube samplers involve substantial inconveniences, safety problems, and functional difficulties. Most obviously, the use of glass brings about the danger of breakage and cutting, both in use while breaking off the ends, and in shipment to the user. Perhaps even more importantly, use of drawn glass tubes involves resealing difficulties, should the sealing caps fit improperly to be mounted improperly by the user. Further, such caps must be of a flexible material of which all the known elastomers have some absorption characteristics with the gases being sampled. In either case, contamination of the charcoal or loss of the trapped gas sample may result by leakage, absorption, or adsorption, thereby obviating the accuracy of the measurements.
In order to avoid contamination or loss of the sample during shipment to an analysis facility, it is often necessary to utilize dry ice containers, which serve to maintain the gases on the charcoal. This method is impractical, costly, incovenient, and inaccurate. Nevertheless, the flexible seal must be used on the tubes because a resealing of the tube by melting would produce too much heat, which would drive off the captured gases. Furthermore, rigid seals are inapplicable, because round glass tubing is neither sufficiently round nor concentric to cooperate effectively with screw seals. A sealed metal container could be used for the tubes, but this introduces air spaces into which entrapped gas could migrate.
Further disadvantages of the glass seal method are the requirement for spring locks, or the like, to hold the charcoal in place in the tube. A further disadvantage is the difficulty of removing the batches of charcoal effectively when the time for analysis occurs.
It is an object of the present invention to provide a gas sampling cartridge which is unbreakable, and effectively reuseable and resealable by recharging with fresh charcoal at the manufacturer thus keeping costs to a minimum.
It is a further object to provide effective yet relatively economical apparatus for holding charcoal in place in the cartridge, during shipment and use.
It is another object to provide air sampling cartidges which may be effectively interconnected one to the other in order to handle heavier concentrations which would saturate one tube, and thereby to meet a large variety of environmental situations.
It is a still further object to provide sealing apparatus and methods whereby relatively unskilled personnel may use the apparatus simply and effectively.
In accordance with the above objects, provision for a reuseable integral sampling tube gives rise to more specific operational features, which relate to reuse of the total package. That is, given a reuseable tube, the possibility is created for a total reuseable package, including tube hardware, absorbent material, and apparatus for holding the absorbent material within the tube. It is accordingly a further object of the present invention to provide a gas sampling configuration which is amenable to direct and total withdrawal of the sampled gases, while maintaining the integrity of the configuration, whereupon the integral configuration may then be reused.